JP2016009659A - Inspection method and inspection device for power storage battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power storage battery inspection method and a power storage battery inspection device capable of determining a deterioration state for which a deterioration factor is specified.SOLUTION: Trivalent cobalt has equivalent potential which is the equivalent potential of a reductive reaction progressing irreversibly and also is less than the equivalent potential of nickel oxide, and a nickel hydride power storage battery is discharged to the extent that the positive electrode potential is not more than the equivalent potential of trivalent cobalt. The rate dQ/dV which is the rate of the variation dQ/dt of the discharged electricity amount to the variation dV/dt of the positive electrode potential is calculated. Deterioration of the nickel hydride power storage battery is determined on the basis of the variation amount to the positive electrode of dQ/dV.

Description

  The present invention relates to a storage battery inspection method and a storage battery inspection apparatus.

  It is known that a storage battery such as a nickel metal hydride storage battery gradually deteriorates in battery characteristics such as a decrease in capacity and an increase in internal resistance due to repeated charging and discharging, for example. In order to inspect the deterioration state of a storage battery that has been repeatedly charged and discharged, various inspection methods and inspection apparatuses have been proposed.

  As a method for detecting the decrease in the discharge capacity, the storage battery to be inspected is discharged to a voltage higher than the discharge end voltage, and the discharge capacity is calculated from the voltage, temperature, and time required for the discharge. An estimation method has been proposed (see, for example, Patent Document 1).

JP 2000-251948 A

However, with the method described above, an approximate determination can be made regarding the deterioration state of the storage battery, but the deterioration factor cannot be determined.
The present invention has been made in view of the above circumstances, and an object thereof is to provide a storage battery inspection method and a storage battery inspection apparatus capable of determining a deterioration state in which a deterioration factor is specified.

Hereinafter, means for solving the above-described problems and the effects thereof will be described.
A storage battery inspection method that solves the above problem is a storage battery inspection method that includes a main active material and a metal compound as an additive, and the metal compound has an equilibrium potential for a reduction reaction that proceeds irreversibly. And having a metal compound equilibrium potential less than the equilibrium potential of the main active material, discharging the storage battery in a range where the positive electrode potential is less than or equal to the metal compound equilibrium potential, and the amount of discharge electricity with respect to the rate of change dV / dt of the positive electrode potential. DQ / dV, which is a ratio of the change rate dQ / dt, is determined, and deterioration of the storage battery is determined from the amount of change of dQ / dV with respect to the positive electrode potential.

  An inspection apparatus for a storage battery that solves the above problem is an inspection apparatus for a nickel-metal hydride storage battery having a positive electrode containing nickel oxide and a conductive metal compound, wherein the metal compound is a reduction reaction that proceeds irreversibly. And the inspection apparatus includes a battery discharge unit for discharging the storage battery and a potential measurement unit for measuring the positive electrode potential of the storage battery. A capacity measuring unit for measuring the discharge capacity of the storage battery; and a rate of change dQ of the storage amount relative to a rate of change dV / dt of the positive electrode potential when the positive electrode potential of the storage battery is discharged within the range of the metal compound equilibrium potential or less. A calculation unit that calculates dQ / dV, which is a ratio of / dt, and a determination unit that determines deterioration of the storage battery from the amount of change of dQ / dV with respect to the positive electrode potential.

  When the battery is operating at a positive electrode potential that exceeds the equilibrium potential of the metal compound as an additive, the metal compound is present in a substantially unreduced state in the storage battery without deterioration. However, when the metal compound is reduced depending on the battery usage, etc., the reduction reaction of the metal compound is irreversible, so the amount of the metal compound before reduction is reduced and the function exhibited by the metal compound before reduction is reduced. To do. According to the above method or configuration, by discharging the storage battery, dQ / dV based on the reduction reaction of the metal compound is calculated in the range of the metal compound equilibrium potential or less. Since the amount of change in dQ / dV is correlated with the amount of reduction of the metal compound, the amount of metal compound before reduction immediately before the inspection can be estimated from the amount of change in dQ / dV. Therefore, it is possible to specify the deterioration factor in the reduction of the metal compound before reduction, and to determine the degree of deterioration according to the amount of the metal oxide before reduction estimated from the change amount of dQ / dV.

  About this storage battery inspection method, based on the correlation data that correlates the maximum value of the change amount of the dQ / dV and the degree of deterioration of the storage battery, the deterioration corresponding to the calculated maximum value of the change amount of the dQ / dV. It is preferable to determine the degree.

  According to the above method, the degree of deterioration of the storage battery is determined using the maximum value of the change amount of dQ / dV. For this reason, compared with the case where the integrated value of dQ / dV in a preset range is used, for example, the influence of the background value can be reduced particularly when the change amount of dQ / dV is small. Therefore, erroneous determination about the degree of deterioration of the storage battery can be suppressed.

In this storage battery inspection method, the main active material is preferably nickel oxide.
According to the above method, the main active material can determine the degree of deterioration of nickel oxide. In the case of a nickel metal hydride storage battery whose main active material is nickel oxide, a metal compound (for example, cobalt) whose valence changes is often used as an additive for improving performance. Therefore, the present invention can be suitably used as compared with other batteries.

  In this storage battery inspection method, the metal compound is a cobalt compound containing trivalent cobalt, and when the dQ / dV is calculated, the range is equal to or lower than the equilibrium potential of the reaction of trivalent cobalt and divalent cobalt. It is preferable to calculate dQ / dV at.

  According to the above method, since dQ / dV based on the reduction reaction of trivalent cobalt to divalent cobalt is calculated, the degree of deterioration that specifies the deterioration factor in the reduction of trivalent cobalt in the nickel-metal hydride storage battery is determined. Can be determined. In the case of a nickel metal hydride storage battery, the reduction of cobalt, which is a conductive agent, greatly affects the output of the battery, so confirming the amount of cobalt reduction as in the above method is about the degree of deterioration of the nickel metal hydride storage battery. It is suitable for determination.

About this inspection method of a storage battery, it is preferable that the positive electrode potential of the storage battery is acquired by measuring a potential difference between a reference electrode inserted into the storage battery and a positive electrode of the storage battery.
According to the above method, since dQ / dV is calculated based on the positive electrode potential, the degree of deterioration can be determined for each cell.

About this storage battery inspection method, it is preferable that the dQ / dV is calculated based on a potential difference between a positive terminal and a negative terminal of the storage battery.
In the above method, since the positive electrode potential is calculated based on the potential difference between the positive electrode terminal and the negative electrode terminal of the storage battery, the inspection can be easily performed as compared with the case where the reference electrode is inserted into the battery.

  With respect to this storage battery inspection method, it is preferable that the storage battery is discharged in a range in which the positive electrode potential is larger than the lower limit potential at which decomposition of water contained in the electrolyte starts and is equal to or lower than the metal compound equilibrium potential.

  In the above method, the storage battery is discharged in a range in which the positive electrode potential is larger than the lower limit potential at which water contained in the electrolytic solution starts to be decomposed, thereby suppressing the generation of hydrogen gas due to the decomposition of the electrolytic solution and the decrease in the electrolytic solution. be able to.

  In the storage battery inspection method for solving the above problem, the metal compound has an equilibrium potential of a reduction reaction that proceeds irreversibly and is lower than the equilibrium potential of the main active material, and the storage battery Is discharged in a range where the positive electrode potential is equal to or lower than the metal compound equilibrium potential, and the deterioration of the storage battery is determined from the amount of change in the positive electrode capacity with respect to the positive electrode potential.

  According to the above method, the amount of change in capacity based on the reduction reaction of the metal compound is calculated within the range equal to or lower than the metal compound equilibrium potential. That is, since the amount of change in capacity is correlated with the amount of reduction of the metal compound, the amount of metal compound before reduction can be estimated from the amount of change in capacity. For this reason, a deterioration factor can be specified for the reduction | decrease of the metal compound before reduction | restoration, and the degree of deterioration can be determined according to the quantity of the metal oxide before reduction | restoration.

  According to the storage battery inspection method and inspection apparatus of the present invention, it is possible to determine a deterioration state specifying a deterioration factor of a storage battery.

The perspective view which shows schematic structure of the battery module which is a test object. (A) is a figure which shows the balance of the positive electrode capacity | capacitance of a nickel hydride storage battery, and a negative electrode capacity | capacitance, (b) is a figure which shows the shift | offset | difference of the capacity balance between several batteries. The schematic diagram which shows schematic structure of the test | inspection apparatus in 1st Embodiment. The flowchart which shows the procedure of the inspection method in the embodiment. The graph which shows the overdischarge curve acquired by the inspection apparatus of the embodiment. The graph which shows the dQ / dV value with respect to the positive electrode potential of an initial stage product and a deteriorated product. The figure which shows typically the deterioration determination data stored in the test | inspection apparatus. The graph which shows the charge condition of the initial stage product and degraded product after repeating pulse discharge. The schematic diagram which shows schematic structure of the inspection apparatus in 2nd Embodiment. The graph which shows the overdischarge curve acquired by the inspection apparatus of the embodiment. The schematic diagram which shows schematic structure of the inspection apparatus of a modification. The graph which shows the overdischarge curve acquired by the inspection apparatus of a modification.

(First embodiment)
Hereinafter, a first embodiment of a storage battery inspection method and inspection apparatus will be described. In this embodiment, the storage battery to be inspected will be described as an example of a nickel-metal hydride storage battery. Moreover, in this embodiment, a nickel metal hydride storage battery is illustrated and demonstrated to the battery module which has several cell.

  A schematic configuration of the battery module 11 will be described with reference to FIG. The battery module 11 includes an integrated battery case 16 having an upper opening and a lid portion 17 that seals the upper opening of the integrated battery case 16. The integrated battery case 16 is provided with a plurality of battery cases 15 by partitioning the inner space with partition walls 18.

  In the battery case 15, an electrode plate group 20 is accommodated together with the electrolytic solution. The electrode plate group 20 includes a plurality of positive electrode plates 21, a plurality of negative electrode plates 22, and a separator 23. The positive electrode plates 21 and the negative electrode plates 22 are alternately stacked with separators 23 interposed therebetween. The battery case 15 houses a positive current collector plate 24 to which the end of the positive electrode plate 21 is joined and a negative current collector 25 to which the end of the negative plate 22 is joined. .

  In this embodiment, the electrode plate group 20 constitutes a single battery 30, a plurality of positive plates 21 constitute a positive electrode, and a plurality of negative plates 22 constitute a negative electrode. In the present embodiment, six unit cells 30 are provided in the integrated battery case 16.

  As shown on the upper left side in FIG. 1, a connection hole 26 used for connecting the unit cells 30 is formed in the upper part of the partition wall 18. The connecting protrusions 27 and 28 protruding from the upper portions of the current collector plates 24 and 25 are connected to each other by spot welding through the connection holes 26, so that the adjacent unit cells 30 are electrically connected in series. Connected.

  As shown in the center of FIG. 1, on both sides in the longitudinal direction of the integrated battery case 16, a positive terminal 29 connected to the battery case 15 at one end and a negative electrode connected to the battery case 15 at the other end. Terminals 32 (see FIG. 3) are provided. A bus bar module (not shown) is connected to each of the positive electrode terminal 29 and the negative electrode terminal 32, and the total output of the six unit cells 30 connected in series is taken out through each bus bar module.

  Next, the positive electrode and the negative electrode will be described. The positive electrode plate 21 has a base material and a positive electrode material supported by the base material. The positive electrode material includes a positive electrode active material mainly composed of nickel oxide such as nickel hydroxide and nickel oxyhydroxide, a conductive agent containing cobalt as a metal compound as an additive (conductive agent), and the like. The discharge reaction of the positive electrode active material is represented by the following half reaction formula (1). At the time of charging, the reaction proceeds in the reverse direction of the half reaction formula (1).

(Positive electrode) NiOOH + H ₂ O + e ⁻ → Ni (OH) ₂ + OH ⁻ (1)
Note that the equilibrium potential of the reduction reaction from trivalent nickel (Ni ³⁺ ) to divalent nickel (Ni ²⁺ ) and the reverse oxidation reaction (hereinafter also referred to as Ni ³⁺ / Ni ²⁺ equilibrium potential or standard potential) is , “0.4 V” with respect to the mercury oxide reference electrode (Hg / HgO). Note that this equilibrium potential depends on the pH of the electrolytic solution and so on, and thus varies depending on the type of battery. Therefore, the “equilibrium potential” of Ni ³⁺ / Ni ²⁺ used in the following embodiments is set to an equilibrium potential of “0.4 V”.

The conductive agent is a cobalt compound such as cobalt oxyhydroxide (CoOOH) and covers the surface of the nickel oxide. In the battery module 11 at the time of shipment, the cobalt compound that coats the surface of the nickel oxide exists in a state containing trivalent cobalt (Co ³⁺ ). Highly conductive cobalt oxyhydroxide forms a conductive network in the positive electrode and increases the utilization factor of the positive electrode (percentage of “discharge capacity / theoretical capacity”).

Cobalt oxyhydroxide is stable within a preset operating voltage range for each cell 30. This is because the equilibrium potential of the reaction in which trivalent cobalt is reduced to divalent cobalt and the reaction in which divalent cobalt is oxidized to trivalent cobalt (hereinafter, both the equilibrium potential of Co ³⁺ / Co ²⁺ and the standard potential). This is because it is “0.1 V” with respect to the mercury oxide reference electrode (Hg / HgO), is smaller than the equilibrium potential of Ni ³⁺ / Ni ²⁺ , and is outside the operating voltage range for each unit cell 30. . In the present embodiment, the equilibrium potential of Co ³⁺ / Co ²⁺ is “0.1 V”. Therefore, as long as the unit cell 30 operates within the operating voltage range, most of the conductive agent is not reduced to cobalt hydroxide or the like. Similar to the “equilibrium potential” of Ni ³⁺ / Ni ^2+, the equilibrium potential of Co ³⁺ / Co ²⁺ also depends on the pH of the electrolyte, and therefore varies depending on the type of battery. Therefore, the “equilibrium potential” of Co ³⁺ / Co ²⁺ used in the following embodiments is set to an equilibrium potential of “0.1 V”.

  The negative electrode plate 22 has a base material and a negative electrode material supported by the base material. The negative electrode material has a negative electrode active material containing a hydrogen storage alloy (MH). The discharge reaction of the negative electrode is represented by the following half reaction formula (2). At the time of charging, the reaction proceeds in the reverse direction of the half reaction formula (2).

(Negative electrode) MH + OH ⁻ → M + H ₂ O + e ⁻ (2)
Reaction at the time of discharge of the entire nickel-metal hydride storage battery is represented by the following half reaction formula (3). At the time of charging, the reaction proceeds in the reverse direction of the half reaction formula (3).

(Overall) NiOOH + MH → Ni (OH) ₂ + M (3)
As shown in FIG. 2A, in the initial state, which is the state when the nickel-metal hydride storage battery is shipped, the negative electrode capacity is set to be positive electrode regulation larger than the positive electrode capacity. Therefore, the negative electrode capacity is provided with a charge reserve R1 and a discharge reserve R2 that are provided in excess of the positive electrode capacity. Therefore, the state in which the SOC of the positive electrode reaches 100% is the state in which the SOC is 100% in the single battery 30 (full charge state). The state in which the SOC of the positive electrode has reached 0%, that is, the state in which the charged part of the active material of the positive electrode has disappeared is the state in which the SOC of the unit cell 30 is 0%.

On the other hand, when charging / discharging of the battery module 11 is repeated, the balance between the positive electrode capacity and the negative electrode capacity in the initial state may change due to factors such as a temperature difference in the battery module 11.
As a result, there is a difference in the balance between the positive electrode capacity and the negative electrode capacity among the plurality of single cells 30 as exemplified by the capacity balance of “single cell A” and “single cell B” in FIG. Sometimes. Thus, when a difference occurs in the balance between the positive electrode capacity and the negative electrode capacity, the SOC of the positive electrode of “single cell B” becomes “0” at the earliest timing with respect to the other single cells 30 at the time of discharging.

By the way, even if the battery module 11 is operated within the set operating voltage range, in the process of repeated charging and discharging, the conductive agent cobalt oxyhydroxide is changed to cobalt hydroxide having divalent cobalt. May be reduced. For example, when the balance between the positive electrode capacity and the negative electrode capacity is different among the plurality of unit cells 30, if the discharge is continued even when the SOC of the positive electrode in one unit cell 30 is lower than 0%, The battery voltage of the battery 30 may be lower than “0.1 V” which is the equilibrium potential of Co ³⁺ / Co ²⁺ . In the present embodiment, the positive electrode potential when the SOC of the positive electrode is 0% is “0.1 V”. It is also conceivable that the battery module 11 operates outside the operating voltage range set by an unintended factor.

  When the amount of reduction from cobalt oxyhydroxide to cobalt hydroxide increases, the conductivity of the positive electrode decreases due to the decrease in trivalent cobalt that forms the conductive network, resulting in decreased discharge capacity, internal DC resistance, etc. An increase in resistance occurs. The decrease in discharge capacity is particularly noticeable during large current discharge. Note that a decrease in battery characteristics such as a decrease in discharge capacity and an increase in internal resistance can also occur due to other factors such as a difference in the balance between the positive electrode capacity and the negative electrode capacity among a plurality of single cells, a decrease in electrolyte, etc. Only by examining the discharge capacity and internal resistance, it is impossible to grasp the cause of the deterioration of the battery characteristics. Further, in order to improve battery characteristics such as a decrease in internal resistance and an increase in discharge capacity of the nickel metal hydride storage battery, it is necessary to grasp the deterioration factor.

  Next, an inspection method for inspecting the degree of deterioration of the nickel-metal hydride storage battery and an apparatus used for the inspection method will be described together with actions. In this inspection method, the deterioration factor to be inspected is specified as a reduction amount of cobalt oxyhydroxide, which is a conductive agent, to cobalt hydroxide and the like, and the reduction amount is determined as a degree of deterioration that is a degree of deterioration. .

  The conditions of the metal compound that can determine the reduction amount as the degree of deterioration are that the reduction reaction of the metal compound is irreversible while the battery module 11 operates, the equilibrium potential is less than the equilibrium potential of the main active material, The equilibrium potential is above the lower limit potential at which water in the electrolyte is decomposed. The term “irreversible” as used herein means that the reduction reaction in which trivalent cobalt is oxidized to divalent cobalt is irreversible under normal battery use conditions. Except when special treatment for oxidizing cobalt is performed.

With reference to FIG. 3, the structure of the test | inspection apparatus 50 which acquires a positive electrode electric potential is demonstrated.
The inspection device 50 includes a reference electrode 51 that measures the positive electrode potentials of the plurality of single cells 30. In the present embodiment, the inspection device 50 has the same number of six reference electrodes 51 as the number of unit cells 30. As the reference electrode 51, one suitable for an electrolytic solution is usually used. In this embodiment, a mercury oxide reference electrode (Hg / HgO) suitable for an alkaline electrolyte is used.

  A voltmeter 52 is connected to each reference electrode 51. In the present embodiment, the inspection apparatus 50 is provided with six voltmeters 52. The voltmeter 52 is connected to the reference electrode 51 and the current collector plate 24 on the positive electrode side of the unit cell 30, and measures the positive electrode potential with respect to the reference electrode 51. The reference electrode 51 and the voltmeter 52 correspond to a potential measuring unit.

  A discharge circuit 53 and an ammeter 54 are connected to the positive terminal 29 and the negative terminal 32 of the battery module 11. The ammeter 54 corresponds to a capacity measurement unit. In addition, the voltmeter 52, the discharge circuit 53, and the ammeter 54 are connected to a deterioration determination device 55. Each voltmeter 52 outputs a signal corresponding to the measured positive electrode potential to the deterioration determination device 55. That is, the deterioration determination device 55 can acquire the positive electrode potential of each unit cell 30.

  The discharge circuit 53 starts and ends the discharge of the battery module 11 connected to the discharge circuit 53 under the control of the deterioration determination device 55. The discharge circuit 53 corresponds to a battery discharge unit.

The ammeter 54 measures a current value flowing through the battery module 11 and outputs a signal corresponding to the measured current value to the deterioration determination device 55.
The deterioration determination device 55 includes a calculation unit 56 that performs calculation for deterioration determination for each unit cell 30. The calculation unit 56 acquires the positive electrode discharge capacity and the positive electrode potential for each cell 30 based on the signal input from the ammeter 54 and the signals input from the plurality of voltmeters 52. In addition, the calculation unit 56 calculates dQ / dV, which is a ratio of the change rate dQ / dt of the discharge capacity (discharge electric quantity) to the change rate dV / dt of the positive electrode potential. dQ / dV indicates a change in discharge capacity per unit voltage, and is used for deterioration determination for each unit cell 30.

  In addition, the deterioration determination device 55 includes a correlation data storage unit 57 in which correlation data 60 is stored. The correlation data 60 is data that associates the amount of change in dQ / dV of the positive electrode with the degree of deterioration of the cell 30, and is the initial state of the cell 30 (initial product) and a plurality of deteriorated cells 30 (deterioration). It is created in advance based on the measurement value acquired using the product.

  Further, the deterioration determination device 55 includes a determination unit 59. The determination unit 59 determines the degree of deterioration of the unit cell 30 based on the correlation data 60 and the dQ / dV calculated by the calculation unit 56. In addition, the deterioration determination device 55 includes, for example, a display or a printer, and is connected to an output device 61 that outputs the deterioration degree of the unit cell 30 by the determination unit 59.

Next, referring to FIG. 4, the procedure of the inspection method will be described together with the operation of the inspection apparatus 50.
First, the battery module 11 is discharged to a discharge end voltage at which the positive electrode SOC becomes 0% (step S1). The discharge end voltage of one unit cell 30 is “1V”, and the discharge end voltage of the battery module 11 is “6V” which is the sum of the discharge end voltages of the six unit cells 30. At this time, discharging may be performed using an apparatus different from the inspection apparatus 50, or the battery module 11 may be connected to the inspection apparatus 50 for discharging. That is, when discharging while measuring the voltage between the terminals of the battery module 11 with a voltmeter (not shown), discharging is performed until the measured value by the voltmeter reaches “6 V” which is the discharge end voltage of the battery module 11. . Further, when the voltmeter 52 of the inspection device 50 is used, for example, discharging is performed until the measured values of the plurality of voltmeters 52 reach “1V”.

  Next, the lid 17 of the battery module 11 is removed, and the reference electrodes 51 are respectively installed in the plurality of single cells 30 from the upper opening of the integrated battery case 16. And while driving the discharge circuit 53, the degradation determination apparatus 55 acquires the positive electrode potential of each of the plurality of single cells 30 (step S2, see FIG. 4).

  In the stage where the battery module 11 has been discharged to the end-of-discharge voltage, if there is a difference in the balance between the positive electrode capacity and the negative electrode capacity between the plurality of single cells 30, the single cell 30 having a positive electrode SOC of 0%. In addition, there may be a unit cell 30 in which the SOC of the positive electrode exceeds 0%. Even in this case, by continuing the driving of the discharge circuit 53, all the single cells 30 are in an overdischarge state in which discharge is performed at a positive electrode potential “0.1 V” or less when the positive electrode SOC is 0%. . In addition, this discharge shall be performed in the range which does not become below the minimum electric potential (-1.1V) from which decomposition | disassembly of the water contained in electrolyte solution begins. By discharging in a range where the positive electrode potential exceeds the lower limit potential, generation of hydrogen and the like accompanying water decomposition, increase in the concentration of the electrolyte, and the like can be suppressed.

  Then, while the overdischarge of the unit cell 30 is continued, the deterioration determination device 55 inputs signals from the ammeter 54 and the plurality of voltmeters 52. And the overdischarge curve which shows the change of the positive electrode electric potential with respect to the discharge capacity of a positive electrode is acquired for every single cell 30 by the calculating part 56 of the deterioration determination apparatus 55 (refer step S3, FIG. 4).

  The discharge curve shown in FIG. 5 is one of the plurality of single cells 30. A broken line indicates a discharge curve indicating a change in positive electrode potential until the SOC of the positive electrode reaches 0%, and a solid line indicates an overdischarge curve indicating a change in potential from the positive electrode potential V1 to a lower limit potential V2 where the SOC of the positive electrode is 0%. is there. In the overdischarge curve, the positive electrode potential suddenly decreases from around the potential V1 “0.1 V” when the SOC of the positive electrode is 0%. This is because cobalt oxyhydroxide is reduced to a compound containing divalent cobalt such as cobalt hydroxide.

As described above, the nickel-metal hydride storage battery is regulated by the positive electrode, and the oxidation reaction of the negative electrode active material proceeds by the discharge reserve of the negative electrode even in the overdischarge state at a potential lower than the potential V1 when the SOC of the positive electrode is 0%. In addition, when the positive electrode SOC is 0% or less when the potential V1 is “0.1 V” or less, the equilibrium potential of Co ³⁺ / Co ²⁺ is less than or equal to the trivalent cobalt contained in the conductive agent. The reduction reaction reduced to cobalt is superior. Note that the reaction amount of the reduction reaction is the largest at a positive electrode potential smaller than the equilibrium potential of Co ³⁺ / Co ²⁺ .

  When the overdischarge curve for each unit cell 30 is acquired, the calculation unit 56 of the deterioration determination device 55 calculates dQ / dV based on the overdischarge curve for each unit cell 30 (see step S4, FIG. 4). Note that the positive electrode potential range or capacity range for calculating dQ / dV in the overdischarge curve is determined in advance through experiments, and the change in dQ / dV is acquired as a curve indicating the change with respect to the positive electrode potential.

As shown by a curve L1 in FIG. 6, in an initial product that is a unit cell 30 without deterioration, electrons are consumed when trivalent cobalt is reduced to divalent cobalt, so that dQ / dV is There is a peak increasing in the negative direction. This peak indicates that the amount of change in dQ / dV is rapidly increasing, and the positive electrode potential range in which the peak appears is a potential range smaller than the equilibrium potential “0.1 V” of Co ³⁺ / Co ^2+. . In the present embodiment, the minimum value of dQ / dV, that is, the maximum value of the change amount of dQ / dV is found near the positive electrode potential of “0.03 V”. The positive electrode potential at which the minimum value of dQ / dV appears is a potential at which the reaction amount of the reduction reaction is maximized. The potential range where the peak appears and the positive electrode potential of the minimum value of the peak become smaller as the current during discharge becomes larger, and in some cases, the potential reaches the potential at which water decomposes. For this reason, the discharge rate is preferably 1C or lower, more preferably 1 / 3C or lower.

  On the other hand, as shown by the curves L2 and L3, in the deteriorated products A and B in which the conductive network becomes sparse due to the decrease in trivalent cobalt, the peak of dQ / dV is very small or the peak itself is not detected. . This is because the cobalt oxyhydroxide constituting the conductive agent has already been reduced to cobalt hydroxide or the like in the stage before the inspection, and the reduction amount in which trivalent cobalt is reduced to divalent cobalt in the overdischarge in the inspection. This is because there are few.

  Next, the determination part 59 of the deterioration determination apparatus 55 acquires the peak value which is the maximum value of the change amount of dQ / dV of the unit cell 30 (see step S4, FIG. 4). The “change amount” here is a change amount from a reference point such as a discharge start time.

  The peak value is the magnitude (absolute value) of the minimum value of dQ / dV within the predetermined positive electrode potential range in the change curve of dQ / dV. In other words, the peak value indicates the maximum height of the peak within a predetermined positive electrode potential range. When almost no peak is observed, the minimum value of dQ / dV in the predetermined positive electrode potential range is regarded as the peak apex, and the absolute value of dQ / dV, which is the minimum value, is set as the peak value. Note that the positive electrode potential range that is the object of calculation of dQ / dV described above includes the average of the range in which the peak of the initial product appears, and the vicinity of the average (for example, from “average value” −0.01 V to “average” Value "+ 0.01V range). In the case of a deteriorated battery, the peak may not appear clearly, but in that case, a part different from the actual peak may be recognized as a peak due to a reaction other than the reduction reaction of cobalt or the background. . However, such a concern is reduced by setting the positive electrode potential range with reference to the peak of the initial product.

Note that the width of the positive electrode potential range may be determined in consideration of the “shift in the positive electrode potential of the peak” that depends on the type of the battery.
The positive electrode potential range is set between the equilibrium potential of Co ³⁺ / Co ^{2+ and} the lower limit potential V2.

  In addition, instead of calculating the peak value of dQ / dV, an integrated value of dQ / dV in a predetermined positive electrode potential range may be calculated. In this case, the reaction other than the cobalt reduction reaction, the influence of the background, etc. Becomes larger. When the deteriorated products are compared with each other, the difference in dQ / dV peak size, width, and the like becomes small. Therefore, when the influence of the background becomes large, accurate determination cannot be made. However, determining the degree of deterioration based on the peak value can reduce the influence of the background and the like, and enables accurate determination.

Next, the degree of deterioration is determined by comparing the peak value acquired in step S5 with the correlation data 60 (step S6, see FIG. 4).
As shown in FIG. 7, the correlation data 60 is an arithmetic expression, a map, or the like in which the deterioration level (%) is associated with the peak value of dQ / dV. In the correlation data 60, the degree of degradation increases as the peak value of dQ / dV decreases.

  In creating the correlation data 60, a pulse discharge of a large current (for example, 25 C) is applied to an initial product that is the unit cell 30 and a plurality of deteriorated units that are known to be deteriorated in advance. The dischargeable SOC is calculated from the SOC after the large current discharge.

  In the example of FIG. 8, the positive electrode potential change with respect to the SOC when the initial product and the deteriorated products C and D are pulse-discharged under the same conditions is shown. For convenience, a curve indicating the positive electrode potential change is a vertical axis indicating the positive electrode potential. The display is shifted in the direction.

  The initial product has 5% SOC after large current discharge, so "95%" is SOC that can be discharged during large current discharge. This initial product is defined as “0% degradation”. In the deteriorated product C, the SOC that can be discharged during the large current discharge is “87%” because the SOC after the large current discharge is 13%. Since the deteriorated product D has an SOC of 19% after a large current discharge, the SOC that can be discharged at the time of the large current discharge is “81%”. Note that the number of deteriorated products used for the correlation data is actually more than two, such as several tens. It can be seen that the deteriorated products C and D have lower SOCs that can be finally discharged than the initial products.

  Furthermore, the degree of deterioration is calculated based on the following formula from the SOC that can be discharged at the time of large current discharge of the deteriorated product. “SOC2” is an SOC that can be discharged during a large current discharge to be inspected, and “SOC1” is an SOC that can be discharged during a large current discharge of the initial product.

Deterioration degree (%) = {1- (SOC2 / SOC1)} · 100

Then, the deterioration determination data of FIG. 7 is created by plotting the peak value of dQ / dV and the degree of deterioration calculated based on the above formula for the initial product and the plurality of deteriorated products.

  Using the correlation data 60 created in this manner, the determination unit 59 of the deterioration determination device 55 acquires the degree of deterioration corresponding to the dQ / dV peak value to be inspected. Then, the deterioration degree is output to the output device 61 as the deterioration degree of the unit cell 30 to be inspected. As described above, in the present embodiment, the degree of deterioration is determined for each unit cell 30, so that a deteriorated product in the battery module 11 can be specified.

As described above, according to the first embodiment, the effects listed below can be obtained.
(1) Since the equilibrium potential of Co ³⁺ / Co ²⁺ is less than the equilibrium potential of Ni ³⁺ / Ni ²⁺ , which is a positive electrode active material, in a nickel-metal hydride battery without deterioration, the conductive agent that covers the positive electrode active material is 3 It is stable in the state of valence cobalt (in this embodiment, cobalt oxyhydroxide). However, when cobalt oxyhydroxide is reduced depending on the usage conditions, the reaction is irreversible, so the amount of cobalt oxyhydroxide decreases, and the conductivity of the positive electrode decreases. According to the present embodiment, dQ / dV based on the reduction reaction of trivalent cobalt is calculated within a range equal to or less than the equilibrium potential of Co ³⁺ / Co ²⁺ . Since the peak value of dQ / dV has a correlation with the amount of trivalent cobalt reduced, the amount of cobalt oxyhydroxide before reduction is reduced from the peak value of dQ / dV without initial deterioration. It can be estimated relative to the product. For this reason, a deterioration factor can be specified for the reduction | decrease of the cobalt oxyhydroxide before reduction | restoration, and a deterioration degree can be determined according to the quantity of the cobalt oxyhydroxide before reduction | restoration. In the case of a nickel metal hydride storage battery, the reduction of cobalt, which is a conductive agent, greatly affects the output of the battery, so confirming the amount of cobalt reduction as in the above method is about the degree of deterioration of the nickel metal hydride storage battery. It is suitable for determination.

  (2) The degree of deterioration of the single battery 30 is determined using the peak value that is the maximum value of the change amount of dQ / dV of the single battery 30. For this reason, compared with the case where the integrated value of dQ / dV is calculated, it is possible to reduce the influence of reactions other than the reduction reaction of cobalt, the background, and the like. For this reason, it is possible to accurately determine the degree of deterioration of the nickel-metal hydride storage battery.

  (3) In the said embodiment, the inspection method using the peak value of dQ / dV was applied with respect to the nickel hydride storage battery whose main active material is a nickel oxide. In a nickel metal hydride battery, a metal compound (for example, cobalt) whose valence changes is often used as an additive for improving performance. Therefore, the present invention can be suitably used as compared with other batteries.

  (4) Reduction of cobalt as the conductive agent greatly affects the output of the nickel-metal hydride storage battery. For this reason, the calculation of dQ / dV below the equilibrium potential of the reaction of trivalent cobalt and divalent cobalt is suitable for determining the degree of deterioration of the nickel-metal hydride storage battery.

  (5) The positive electrode potential is acquired by measuring the voltage (potential difference) between the reference electrode 51 inserted in the single cell 30 and the positive electrode of the single cell 30. That is, since dQ / dV is calculated for each unit cell 30, the degree of deterioration can be determined for each unit cell 30.

  (6) Since the unit cell 30 is discharged from the positive electrode potential where the SOC of the positive electrode is 0% to the lower limit potential at which the water of the electrolytic solution is decomposed, the generation of hydrogen based on the decomposition of the electrolytic solution and the electrolysis A change in the concentration of the liquid can be suppressed.

(Second Embodiment)
Next, a second embodiment embodying the present invention will be described. In addition, since 2nd Embodiment is the structure which changed a part of test | inspection apparatus of 1st Embodiment, it attaches | subjects the same code | symbol about the same part, and abbreviate | omits the detailed description.

  As shown in FIG. 9, the inspection device 50 of the present embodiment includes a voltmeter 52 that measures the voltage between the positive terminal 29 and the negative terminal 32 of the battery module 11. Further, the inspection device 50 includes an ammeter 54 that measures a current flowing through the battery module 11. The voltmeter corresponds to the potential measurement unit, and the ammeter corresponds to the capacitance measurement unit.

  Further, the inspection device 50 includes a discharge circuit 53 and a deterioration determination device 55 as in the first embodiment. That is, this embodiment is different from the first embodiment in that the positive electrode potential is not measured for each unit cell 30 but the voltage of the battery module 11 is measured, and the procedure of the inspection method is basically the first. This is the same as the embodiment.

  As shown in FIG. 10, the deterioration determination device 55 drives the discharge circuit 53 to discharge the battery module 11 and inputs signals from the voltmeter 52 and the ammeter 54 to obtain a discharge curve. As described above, when the balance between the positive electrode capacity and the negative electrode capacity is different among the plurality of single cells 30 (see FIG. 2B), the timing at which the SOC of the positive electrode becomes 0% is different. For this reason, in this embodiment, the discharge end voltage “6V” of the battery module 11 is used as a reference, and “8.0 V” (the voltage at which the positive SOC of any single battery 30 does not reach 0%) near the discharge end voltage. Discharge is performed at a high discharge rate, and then discharged at a low discharge rate. When the SOC of the positive electrode of one unit cell 30 among the plurality of unit cells 30 becomes 0%, a rapid voltage drop occurs, and the voltage drop amount of the battery module 11 with respect to the discharge capacity increases.

  For this reason, the calculating part 56 of the degradation determination apparatus 55 detects the area | regions Z1-Z6 where the voltage drop amount of the battery module 11 with respect to discharge capacity is more than the preset voltage drop rate among the acquired overdischarge curves. And the calculating part 56 makes these area | regions Z1-Z6 the battery voltage in which SOC of the positive electrode of the cell 30 became 0%, respectively. At this time, since the voltage drop amount of one unit cell 30 is substantially constant, the region where the voltage drop amount is large is less than the number of the unit cells 30 and the voltage drop amount is large, the voltage in that region is large. The number of single cells 30 in which the SOC of the positive electrode becomes 0% is determined by dividing the amount of drop by the average of the amount of voltage drop of the single cells. For example, when it is determined that the number of single cells 30 is two, the region where the voltage drop amount is large is divided into two.

The calculation unit 56 calculates dQ / dV based on the voltage change on the assumption that the voltage change with respect to the capacitance in the regions Z1 to Z6 corresponds to the potential change of the positive electrode potential below the equilibrium potential of Co ³⁺ / Co ²⁺ . And the calculating part 56 makes this the dQ / dV value of the some cell 30. FIG. Further, the calculation unit 56 calculates the peak value of the dQ / dV value in the regions Z1 to Z6, refers to the correlation data 60, and determines the degree of deterioration of the unit cell 30.

  In this method, even if the degree of deterioration of the unit cell 30 is determined, it cannot be specified which unit cell 30 corresponds to the degree of deterioration. However, the unit cell 30 belonging to the battery module 11 is trivalent. Whether or not deterioration due to a decrease in cobalt has occurred, and when deterioration has occurred, the degree of deterioration can be grasped. Moreover, since it can test | inspect without removing the cover part 17 of the battery module 11, compared with the case where the cover part 17 is removed, it can test | inspect easily.

As described above, according to the second embodiment, in addition to the effects (1) to (4) and (6) described in the first embodiment, the effects listed below can be obtained.
(7) In this embodiment, dQ / dV is calculated based on the voltage between the positive terminal 29 and the negative terminal 32 of the battery module. In this case, since it is not necessary to remove the lid portion 17 of the battery module 11, the inspection can be easily performed as compared with the case where the reference electrode 51 is inserted into the single battery 30.

In addition, each said embodiment can also be suitably changed and implemented as follows.
In each of the above embodiments, the unit cell 30 constituting the battery module 11 is the inspection target, but other unit cells may be the inspection target. Even in a unit cell, the metal compound (for example, cobalt) as an additive contained in the positive electrode of the unit cell 30 may decrease due to unintended factors such as operation outside the operating voltage range. When a single cell is to be inspected, for example, as shown in FIG. 11, a reference electrode 51 is inserted into the single cell 30, and a discharge circuit 53 and an ammeter 54 are connected to the positive electrode terminal 71 and the negative electrode terminal 72, A discharge circuit 53 and an ammeter 54 may be connected to the positive terminal 71 and the reference electrode 51 of the unit cell 30. Alternatively, the terminal voltage between the positive electrode terminal 71 and the negative electrode terminal 72 may be measured without using the reference electrode, and the positive electrode potential may be estimated from the value. The inter-terminal voltage is the difference between the positive electrode potential and the negative electrode potential. If the negative electrode potential is known, the positive electrode potential can be estimated from the inter-terminal voltage. In the case of a nickel metal hydride storage battery, since the potential of the negative electrode is substantially constant, the positive electrode potential can be estimated relatively easily from the voltage between the terminals.

  In each of the above embodiments, the degree of deterioration of the cell 30 is determined using the amount of change in dQ / dV, but as shown in FIG. 12, a voltage drop occurs from the potential when the SOC of the positive electrode is 0%. The degree of deterioration of the unit cell 30 may be determined based on the change amount ΔC of the discharge capacity during the period. This amount of change in the discharge capacity corresponds to the peak area of dQ / dV during the voltage drop. According to this method, the amount of calculation of the deterioration determination device 55 can be reduced.

  In each of the above embodiments, the degree of deterioration of the single battery 30 is determined using the peak value of dQ / dV, but the degree of deterioration may be determined using a value related to dQ / dV other than the peak value. For example, in the case of a battery having a particularly high degree of deterioration, when the influence of background or the like can be reduced, the degree of deterioration may be determined using the peak area of dQ / dV. Alternatively, the degree of deterioration of the unit cell 30 may be determined using an absolute value of dQ / dV of a positive electrode potential determined in advance.

In each of the above embodiments, the discharge circuit 53 is controlled by the deterioration determination device 55. However, the drive may be started and ended separately from the deterioration determination device 55.
The deterioration determination device 55 may include at least one of the discharge circuit 53, the ammeter 54, and the voltmeter 52.

In each of the above embodiments, the deterioration factor is specified as a decrease in trivalent cobalt, but may be specified as a decrease in other metal compounds as long as a predetermined condition is satisfied. Predetermined conditions are that “the reduction reaction of the metal compound is irreversible while the storage battery operates when the SOC of the positive electrode is between 0% and 100%”, “the equilibrium potential is less than the equilibrium potential of the positive electrode active material It is an element satisfying “being higher than the lower limit potential at which water is decomposed” or a compound containing the element. Further, the metal compound is not limited to the conductive agent, and may be included in additives such as a secondary active material and a binder. In addition, “irreversible” indicates that the reaction is irreversible in a normal battery use state, and does not indicate that the state does not return to the state before reduction even if a special oxidation treatment or the like is performed. For example, examples of the metal compound capable of inspecting the degree of deterioration include compounds containing the following metal elements. In the following parentheses, the metal element on the left indicates the normal state, and the metal element on the right indicates the overdischarge state. Molybdenum (Mo ⁴⁺ → Mo: equilibrium potential −0.9 V to −1.0 V), titanium (Ti ⁵⁺ → Ti ³⁺ : equilibrium potential −0.9 V to −1.0 V), niobium (Nb ⁵⁺ → Nb ⁴⁺ : equilibrium Potential -1.0V to -1.1V), cadmium (Cd2 ⁺ → Cd: equilibrium potential -0.8V to -0.9V), iron (Fe3 ⁺ → Fe: equilibrium potential -0.7V to -0.9V) ), Manganese (Mn ⁶⁺ → Mn ²⁺ : equilibrium potential −0.4 V to −0.2 V), vanadium (V ³⁺ → V ²⁺ : equilibrium potential −0.7 V to −0.6 V), tantalum (Ta ⁵⁺ → Ta : Equilibrium potential −0.9 V to −1.7 V), tungsten (W ⁸⁺ → W ⁶⁺ : Equilibrium potential +0.3 V to +0.4 V). The equilibrium potential of each substance is based on a standard hydrogen electrode.

  -The storage battery to be inspected may be other than the nickel metal hydride storage battery. For example, a nickel-cadmium storage battery using nickel oxide as a positive electrode active material or a lithium ion storage battery using cobalt lithium oxide as a positive electrode active material may be used.

  DESCRIPTION OF SYMBOLS 11 ... Battery module as a storage battery, 21 ... Positive electrode plate which comprises a positive electrode, 22 ... Negative electrode plate which comprises a negative electrode, 23 ... Separator containing electrolyte solution, 29 ... Positive electrode terminal, 30 ... Single cell as a storage battery, 32 ... Negative terminal, 50 ... inspection device, 51 ... reference electrode as potential measurement unit, 52 ... voltmeter as potential measurement unit, 53 ... discharge circuit as battery discharge unit, 54 ... ammeter as capacity measurement unit, 56 ... Calculation unit, 59 ... determination unit, 60 ... correlation data.

Claims (9)

In a storage battery inspection method including a main active material and a metal compound as an additive,
The metal compound has an equilibrium potential of a reduction reaction that proceeds irreversibly and is less than the equilibrium potential of the main active material,
The storage battery is discharged in a range where the positive electrode potential is equal to or lower than the metal compound equilibrium potential, and dQ / dV which is a ratio of the rate of change dQ / dt of the discharge electricity amount to the rate of change dV / dt of the positive electrode potential is calculated, and the dQ A storage battery inspection method, wherein deterioration of the storage battery is determined from a change amount of / dV with respect to the positive electrode potential. The degree of deterioration corresponding to the calculated maximum value of the change amount of the dQ / dV is determined based on correlation data in which the maximum value of the change amount of the dQ / dV is associated with the degree of deterioration of the storage battery. The inspection method of the storage battery as described in 2. The storage battery inspection method according to claim 1, wherein the main active material is nickel oxide. The metal compound is a cobalt compound containing trivalent cobalt,
The method for inspecting a storage battery according to claim 3, wherein when calculating dQ / dV, dQ / dV in a range equal to or lower than an equilibrium potential of a reaction between trivalent cobalt and divalent cobalt is calculated. The method for inspecting a storage battery according to claim 1, wherein a positive electrode potential of the storage battery is acquired by measuring a potential difference between a reference electrode inserted into the storage battery and a positive electrode of the storage battery. The storage battery inspection method according to claim 1, wherein the dQ / dV is calculated based on a potential difference between a positive electrode terminal and a negative electrode terminal of the storage battery. The storage battery according to any one of claims 1 to 6, wherein the storage battery is discharged in a range in which a positive electrode potential is greater than a lower limit potential at which decomposition of water contained in the electrolyte starts and is equal to or lower than the metal compound equilibrium potential. Inspection method. In a storage battery inspection method including a main active material and a metal compound as an additive,
The metal compound has an equilibrium potential of a reduction reaction that proceeds irreversibly and is less than the equilibrium potential of the main active material,
The storage battery is discharged in a range where the positive electrode potential is equal to or lower than the metal compound equilibrium potential, and the deterioration of the storage battery is determined from the amount of change in the positive electrode capacity with respect to the positive electrode potential. In an inspection device for a storage battery containing a main active material and a metal compound as an additive,
The metal compound has an equilibrium potential of a reduction reaction that proceeds irreversibly and is less than the equilibrium potential of the main active material,
The inspection device includes:
A battery discharger for discharging the storage battery;
A potential measuring unit for measuring the positive electrode potential of the storage battery;
A capacity measuring unit for measuring the discharge capacity of the storage battery;
An arithmetic unit for calculating dQ / dV, which is a ratio of the rate of change dQ / dt of the amount of discharge electricity to the rate of change dV / dt of the positive electrode potential when the positive electrode potential of the storage battery is discharged within the range of the metal compound equilibrium potential or less. When,
A determination unit that determines deterioration of the storage battery from a change amount of the dQ / dV with respect to the positive electrode potential.

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